Device for raising weights in precision balances

ABSTRACT

Device for raising weights in precision balances, such as analytical balances, in which a number of weights from the smallest to the largest are disposed substantially in a single plane and are made associated with at least two pusher raising elements mobile in a direction substantially orthogonal to the plane of the weights, the pusher raising elements being raised by programmed operating means including rotatable annular disc members and cam means provided thereon. The disc members are rotated by acting on the weighing control members of the balance.

United States Patent 1 1 1111 3,842,925 Crespi 1 1 Oct. 22, 1974 [5DEVICE FOR RAISING WEIGHTS IN 3,004,618 l0/l96i Meier 177/248 PRECISIONBALANCES 3,026,954 3/1962 Appius 177/248 Carlo Crespi, Via Sordello 10.Milan, Italy Filed: Oct. 3, 1972 Appl. No.: 294,736

Inventor:

Foreign Application Priority Data Oct. 5. 1971 Italy 53269 ReferencesCited UNITED STATES PATENTS 9/1956 Mettler 177/191 8/1960 Rapp ..177/203Primary Examiner-Richard B. Wilkinson Assistant Examiner-Vit W. MiskaAttorney, Agent, or FirmGuido Modiano; Dr. Albert Josif [57] ABSTRACTDevice for raising weights in precision balances. such as analyticalbalances, in which a number of weights from the smallest to the largestare disposed substantially in a single plane and are made associatedwith at least two pusher raising elements mobile in a directionsubstantially orthogonal to the plane of the weights, the pusher raisingelements being raised by programmed operating means including rotatableannular disc members and cam means provided thereon. The disc membersare rotated by acting on the weighing control members of the balance.

6 Claims, 9 Drawing Figures DEVICE FOR RAISING WEIGHTS IN PRECISIONBALANCES BACKGROUND OF THE INVENTION The present invention relates to adevice for raising and lowering weights in precision balances.

Precision balances, for example analytical balances, comprise a certainnumber of weights suspended at one end of the balance arm and acounterweight disposed at the opposite end of the arm, in such a manneras to exactly balance the balance. During the act of weighing, afterhaving disposed the mass to be weighed on the plate lying below theweights and the balance has been thrown out of balance a number ofweights are raised equivalent to the weight placed on the plate so as toagain balance the balance. This operation is carried commonly out byhooks controlled by levers, which take each weight and raise it so thatit no longer bears on the arm of the balance. A set of knobs is providedfor controlling the levers, and their rotation causes movement of thelevers by the action of corresponding means such as cams etc.

As the sensitivityof the balance increases, i.e., as the number ofsignificant figures of weight determinable by the balance increases, thetotal number of weights also increases, these having then to be disposedin a number of groups sufficiently separated in order to enable thehooks and levers to correctly operate without interference.

The weights are hence disposed along a number of axes or horizontalplanes one below the other, so as to limit the number of weights in eachplane and make possible the raising operations for all weights from themechanical point of view.

In the case of precision balances this arrangement, which is universallyadopted, limits the sensitivity of the balance and introduces a factorof uncertainty and error, which become more significant as the precisionof the balance increases.

When weighings are required to the order of four or five decimal placesit becomes necessary also to consider the influence of atmosphericpressure at the various heights at which the weights are disposed.

The weights, calibrated exactly under the same conditions, no longerrigorously give the same value if disposed at different heights and thisobviously influences the weighing precision to an extent which cannot bepreviously determined for each weight, and it is thus not possible togive an exact correction factor for correcting the weighing each time.This means that even the most sensitive balances always have a certaintolerance, even though small, which is imputable to this fact.

To this must be added the mechanical complexity of the system forraising the weights when these exist in great number and have to bedisposed on a number of planes, and the fact that the weight is notraised perfectly vertically as is desirable, but through a certain arebecause of the fact that the levers are necessarily pivoted at a fixedfulcrum of the balance.

SUMMARY OF THE INVENTION An object of the present invention is toovercome the aforementioned disadvantages of known precision balances byproviding a device for raising the weights which firstly introduces nopossibility of error in weighing, even in the case of extremely smallweighings, and

furthermore leads to a considerable reduction, for like numbers ofweights, in the overall bulk of these latter and simplification of themeans for raising the weights.

Another object of the invention is to provide a device easily installedon precision balances and of durable operation.

These objects are attained by a device for raising weights in precisionbalances in which all the weights from the smallest to the largest aredisposed substantially in a single plane and are each associated with atleast two pusher raising elements mobile in a direction substantiallyorthogonal to the plane of the weights, the pusher elements being raisedby programmed operating means associated respectively with the weighingcontrol members of the balance.

BRIEF DESCRIPTION OF THE DRAWINGS Further particulars andcharacteristics of the invention will be more evident from the followingdetailed description of a preferred embodiment of the invention,illustrated by way of example in the accompanying drawings in which:

FIG. 1 is a diagrammatic lateral view of a precision balance to whichthe device of the invention is applied;

FIG. 2 is a partially exploded view of the device of the invention;

FIG. 3 is a view from above of the balance of FIG. 1 without the cover;

FIG. 4 is a plan view of the means for the programmed raising of theweights;

FIG. 5 is a section on the line VV of FIG. 4',

FIG. 6 is a part of the support for the weights;

FIG. 7 shows a detail on an enlarged scale of the pusher elements forraising the weights;

FIG. 8 is a lateral view of the clamping device for the means for theprogrammed raising of the weights; and

FIG. 9 shows a detail of the balance arm.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the example considered herethe device 1 according to the invention is imagined applied to ananalytical balance which in known manner comprises at its lower frontpart the compartment with the weighing plate 2 and in its upper part theactual members of the balance.

The balance beam 3 is supported through the central fulcrum 4 by thecolumn 5 and is provided with the counterweight 6 and air damper 7 atone end and the.

group of annular weights 8 at the other end, from which the plate 2 isalso suspended. The groups of weights, which will be described in detailhereinafter, is suspended from the balance beam 3 by way of the rods 9fixed to the cross member 10, which comprises a lower a lapped surfacefor support on the block 11, which is provided as a lateral fulcrum onthe balance beam 3 at the same distance from the fulcrum 4 as thecounterweight 6. The weighing operation is carried out by manuallyoperable control means such as knobs 12, 12a and 13, 130 by way ofappropriate transmission devices 14 which will be described in greaterdetail hereinafter.

According to the invention all the annular weights, from the smallest tothe largest, are disposed concentrically in the same horizontal plane,and supported in this plane by the arms 15 disposed at one to the otherto constitute the support member for the weights. The

arms 15 comprise notches 16 of a number corresponding to the number ofthe weights and ofa suitable shape and size for seating the weightaccording to its size and they converge at the central body 18, to whichthe rods 9 are fixed, The weights are disposed in increasing order fromthe centre and in the example under consideration they are thefollowing: two weights of 100 mg, one of 200 mg, one of 500 mg, twoweights of l g, one of 2 g, one of g, two weights of g, one of 20 g, oneof 50 g, and one weight of 100 g. in this manner there is a total of 13weights whose sum total is I99.900 g. It is to be understood howeverthat their number and value could be different.

Immediately below the plane of the weights but free from it, the device1 comprises the pusher elements and the operating means for theprogrammed raising of the weights, indicated overall by the referencenumeral 20. More precisely the device 1 comprises a base 21 ofcylindrical form, to whose lateral surface 22 are fixed at 90 one to theother the supports 23, provided at their free end with a notch 24 inwhich is clasped the corresponding end of the transverse stop bars 25,whose form is visible inFlG. 5 and against which the raised weightsengage. The crosspieces 26 and 27 are fixed to the supports 23 below thebars and define guiding means in which pins 28 and 29 are slidable in adirection orthogonal to the plane of the weights 8. The pins 28 and 29constitute the pusher elements for raising the weights and aredistributed in such a manner that each pair of diametrically opposingpins supports a single annular weight, the pairs being alternatedbetween one crosspiece and the other as passage is made from one weightto the next. The means for the programmed operation of the pins compriserotatable annular disc members or programming plates 30, 31, 32 and 33,which each comprise on their upper face as series of profiles or cams 34disposed according to a precise programme, and on their lower faceoperating means including a respective annular too thing 35 which mesheswith three gearwheels 36, disposed at 120 one to the other. One of thegearwheels 36 of each plate is fixed rigidly to a shaft 37 which emergesfrom the lateral surface 22 of the base 21 and comprises a bevel gear38, operatively connected to the knobs 12, 12a and 13, 13a. The othergearwheels 36 of each plate are fixed to respective shafts housed idlyin the lateral surface 22 and in the central part 40 of the base 21 andserve exclusively as a support for the programming plates, which thusalso lie in a single plane as the weights 8. The disposition of thevarious gearwheels below the programming plates, and of all othertoothed wheels for the operation of the programming plates, is shown inFIG. 3 in which the details above the plates and the weights have beenomitted. The entire device 1 is removably mounted on the shelf 41 of thebalance.

The internal programming plates 31, 32 33 have ten cam profiles orportions which are repeated identically over the angular development ofeach of them. The most external plate 30 has instead a different profileand comprises only four cam portions. For this reason only the form ofthe profiles ofthe plates 31 and 30 will be described hereinafter.

In the example described and shown, with each of the internalprogramming plates 31, 32 and 33 are associated four weights, multiplesof 10 of the two weights of I00 mg, of that of 200 mg and of that of 500mg. With this values of weights it is possible, as is known, to definean entire weight decade. With the external plate 30 is associated asingle weight of 100 g. One turn of the programming plates 31, 32 and 33corresponds to an entire weighing are from 1 to 9 100-900, [0-90) plusthe position 0, so as to obtain all the weight values which aremultiples of 100 mg. in order to obtain this each of the plates 31, 32and 33 has the profiles 34 disposed on five concentric circumferences,the profiles being diametrically symmetrical in pairs. The plate 31 hasthus two sections 310 acting on the pins situated below the first weightof IO g, two sections 311) and two sections 310 acting on the pinssituated below the second weight of 10 g, two sections 31d acting on thepins corresponding to the weight of 20 g and finally a cam portion 31cand a cam portion 31f, both for raising the weight of 50 g, but situatedon different circumferences. This latter weight must in fact be heldlowered for one half of a turn and raised for the other half, so that asingle cam acting on diametrically opposed pins could not cause the pinsto be either both raised or both lowered. There are consequently twoseparate cams acting each over one half of a turn on one pin so as tosimultaneously carry out the same operation. To this end one of therelative pins has its upper end eccentric with respect to its lower end(FIG. 7).

The external programming plate 30 comprises two sections 30b and 30crelative to the weight of 100 g, disposed angularly distanced as thesections 311) and 310 of the plate 31. The drawings show also thecorresponding sections 32a, 32b, 32c, 32d, 32e and 32f and the sections33a, 33b, 33c, 33d, 33e and 33fof the profiles of the plates 32 and 33.

The length of the individual sections of the profiles is such that foreach angle of rotation of 36 of the plate, an increase in weight of onerelative unit is obtained, in the succession described hereinafter.

Considering for example the plate 31 and the position in which all thepins are lowered, with a first rotation of 36 will correspond theintervention of the section 310 and the raising of the pins 29 of thefirst weight of 10 g. During a further rotation of 36 the section 31awill remain active and the section 311) will intervene and cause theraising of the second l0 g weight by the pins 28, arranged at 90 tothose which keep the first 10 g weight raised. There is thus a total of20 g raised. During a further rotation of 36 the section 31b is nolonger active and the second l0 g weight descends, whereas the first iskept raised by the section 310, and the 20 g weight is raised by theintervention of the section 31d. There is now a total of 30 g raised. Onrotation through a further 36 the section 31c intervenes, and raises thesecond l0 g weight, while the 10 and 20 g weights are kept raised by theremaining sections 310 and 31d. There is now a total of 40g. On afurther rotation of 36 all the weights raised up to now by the sections310, 31c and 31d descend and the sections 3le and 31f intervene, andsimultaneously raise the two pins of the 50 g weight. There is now atotal of 50 g. Proceeding further, as the profiles are diametricallysymmetrical and up to this point one half of a turn has been made, thenfor every 36 of rotation the previous operations will be repeated, withthe difference that the 50 g weight will always remain raised. Thus 60g, g, g and g are obtained in succession, after which the last rotationof 36 will return all the pins to rest and cause all the weights todescend.

It is evident that the same phases will occur by operating the plates 32and 33, but in this case the weights will proceed from 100 mg to 900 mgand from 1 g to l0 g respectively.

The last weight of 100 g requires only two positions, one raised and onelowered, and hence the profiles of the external plate 30 comprise insubstance two sections 30b and 30c separated by 72, so as to give aposition of 0 between two raising positions.

The weights and the positions of the plates and pins shown in thedrawings are those relative to a hypothetical weighing of 170.600 g.

In all these operations the raised weights are made to lightly touch thetransverse bars 25 with a slight pres sure.

To this end the pins are advantageously composed (FIG. 7) of a lowershank 42 rigid with a body 43 of substantially cup form guided in acorresponding seat 44 in the cross bars 26 and 27 respectively, and anupper shank 45 mobile in the body 43 and supported by a spring 46inserted in the body 43. One of the two pins for raising weights whichare multiples of 500 mg is eccentric, as stated, and it comprise twoshanks 42 and 45 olT-centre in the body 43a.

The presence of the spring enables the efiect of the impact of theweights against the bars 25, which could damage the weights, to bedampened, and simultaneously makes the operation of the programmingplates more smooth. When the balance is at rest the weights supported bythe arms are all engaged with the bars, even if the pins are alllowered.

Rotation of the programming plates by the bevel gears 36 takes place byway of the knobs 12, 12a and 13, 130, each of which (FIG. 3) isassociated with one ofthe programming plates. The knobs l2 and 13 act byway of the gearwheels 47 and 48 rigid with the shafts on which the knobsare fixed, and the gearwheels indicated generally by the referencenumerals 49 and 50 on the bevel gears 36 of the plate 33 and 30,respectively. The knobs 12a and 13a act by way of the gearwheels 51 and52, rotably rigid with these knobs, on the gearwheel assembliesindicated generally by the reference numeral 53 and 54, respectively,with which the remaining plates 31 and 32 are associated. Advantageouslysnap action devices are provided consisting of notched wheels 55 andsprings 56 engaged with these notches for the rotation of the knobsthrough a predetermined angle and their exact arrest in each weighingposition. The transmission 47-54 is so calculated in the ratios of thedifferent gearwheels that with one turn of each programming plate therecorresponds one turn of the corresponding knob, so that the snap actiondevices act on each 36 of rotation both of the knobs and of theprogramming plates, so defining without any possibility oferror theexact position in which each weight is perfectly raised or lowered andnot in an intermediate position. With the knobs are associated circularscales numbered from 0 to 9, by which it is possible to directly readthe weighing value on a suitable panel at the front of the balance. Thescales are one within the other on each side, so as to give the valuesin the exact order of reading from left to right.

Each weighing position can be locked by the locking device shown in FIG.8. This is arranged on the shelf4l of the balance in a positioncorresponding with a cavity 57 in the base 21 and comprises four pins58, one under each plate, designed to enter relative dead holes 58aprovided under the plates at a distance one from the other of 36,starting from a predetermined position. The pins 58 are fixed to a platesupport 59 which is mobile above the bracket 60, fixed to the shelf 41of the balance, and comprises guide pins 61 passing through suitableholes 62 in the bracket 60. For raising the pins 58 a lever 63 isprovided pivoted at 64 on the shelf 41 of the balance, and acts on thewheel 65 carried by the rod 66 screwed into the plate support 59 andguided in the sleeve 67 fixed to the bracket 60. The springs 68,arranged between the bracket 60 and enlarged end of the pins 61, removethe pins 58 from their engagement in the dead holes 58a of theprogramming plates. Control of the locking device is by the rod 69operating connected to the lever 70 disposed in the lower front part ofthe balance.

For further increasing the sensitivity of the balance, an optical systemmay be provided for reading the last figures of the weighing, andcomprising (FIG. 3) a graduated scale disposed on the arm 3 in axis withthe luminous ray produced by the lamp 73, and a fixed mirror 76 forreflecting the luminous ray coming from lamp 73 through lenses 74 and 75on to a vernier scale provided on a suitable panel in the upper frontpart of v the balance. With this fixed mirror and vernier system thepossibility of errors in reading the weighing is considerably reduced.

From the description given it can be understood that with the deviceaccording to the invention the objects initially stated are attained. Inparticular the disposition of the weights eliminates with certainty anyerror due to pressure differences and, together with the disposition ofthe entire control assembly, considerably reduces the overall size ofthe device.

Various modifications may be made to the device described within theinventive concept, without leaving the scope of the inventive idea. Thusthe device may be applied to types of precision balances different tothat illustrated and wherever greater weighing precision and lowerconstructional cost is required, for example in the field of technicalbalances, and furthermore the various control means and means forraising the weights may be modified according to requirements. In anadvantageous solution, a control system is provided having all pinsrigid with one plate, which is raised according to a programme by camssuitably set to raise the various weights in succession. In this case afixed programming plate is provided, in which a number of holes aredisposed in accordance with a set pro gramme, so that the underlyingplate carrying the pins brings a certain number of pins under therelative holes in the fixed programming plate for each section ofrotation, and when raised pushes the pins into these holes, so raisingthe relative weights, while the pins not aligned with the holes remaininactive.

I claim:

I. A device for raising and lowering the weights in precision balancesof the type having a balance beam, a support member suspended at one endof said balance beam, a plurality of annular weights supported by saidsupport member concentrically to each other in a substantiallyhoriziontal plane, and manually operable control means for controllingthe raising and lowering of said weights, the device comprising a basefor removable connection to said balance below said support member,guiding means provided over said base and extending below said weightssubstantially radially thereto, a plurality of pusher elements includingpins slidable within said guiding means substantially perpen dicularlyto the plane of said weights for raising and lowering said weights,means for operating said pins including rotatable annular disc membersarranged concentrically to each other in the same plane below saidguiding means and having an upper face provided with cam means forengaging said pins and a lower face provided with operating means forindependent rotation of said disc members, said operating means beingoperatively connected to said manually operable control means of thebalance, whereby operation of said control means causes rotation of saiddisc members and raising and lowering of said weights according to aprogram defined by said cam means.

2. A device as claimed in claim 1, wherein said operating means forindependent rotation of said disc mem bers comprise an annular toothingprovided on the lower face of each of said disc members concentricallythereto, each of said toothings being operatively connected to saidmanually operable control means of the balance by means of gearing.

3. A device as claimed in claim 1, wherein with at least one of saiddisc members there are associated four weigths having respective valuescapable of defining an entire weight decade, and wherein said cam meansare arranged on the upper face of said disc members along concentricannular paths, said cam means having cam portions located along saidpaths at angularly spaced of 36 or multiples thereof, whereby after onecomplete turn of said disc member all the weights of the entire weightsdecade have been raised.

4. A device as claimed in claim I, wherein said guiding means comprisetwo crosspieces arranged at right angles to each other in asubstantially horizontal plane above said disc members, said crosspieceseach having pairs of through bores for receiving respective pairs ofsaid pins, each pair of said pins engaging one of said weights atdiametrically opposite points, the pairs of pins relative to adjacentweights being disposed alternatively in the one and the other of saidcrosspieces.

5. A device as claimed in claim 1, wherein at least one of said discmembers has an external cam comprising two cam portions arrangedopposite to each other along annular concentric pathes of slightlydifferent radii and each extending for a half of its circumference, witheach of said cam portions being associated one pin comprising an upperand a lower shank, the shanks of one of said pins being coaxial to eachother and the shanks of the other of said pins being off-centered,whereby the said upper shank engages the corresponding one of saidannular weights and the said lower shank engages the corresponding oneof said two cam portions.

6. A device as claimed in claim 5, further comprising a springinterposed between said upper and said lower shank.

1. A device for raising and lowering the weights in precision balancesof the type having a balance beam, a support member suspended at one endof said balance beam, a plurality of annular weights supported by saidsupport member concentrically to each other in a substantiallyhoriziontal plane, and manually operable control means for controllingthe raising and lowering of said weights, the device comprising a basefor removable connection to said balance below said support member,guiding means provided over said base and extending below said weightssubstantially radially thereto, a plurality of pusher elements includingpins slidable within said guiding means substantially perpendicularly tothe plane of said weights for raising and lowering said weights, meansfor operating said pins including rotatable annular disc membersarranged concentrically to each other in the same plane below saidguiding means and having an upper face provided with cam means forengaging said pins and a lower face provided with operating means forindependent rotation of said disc members, said operating means beingoperatively connected to said manually operable control means of thebalance, whereby operation of said control means causes rotation of saiddisc members and raising and lowering of said weights according to aprogram defined by said cam means.
 2. A device as claimed in claim 1,wherein said operating means for independent rotation of said discmembers comprise an annular toothing provided on the lower face of eachof said disc members concentrically thereto, each of said toothingsbeing operatively connected to said manually operable control means ofthe balance by means of gearing.
 3. A device as claimed in claim 1,wherein with at least one of said disc members there are associated fourweigths having respective values capable of defining an entire weightdecade, and wherein said cam means are arranged on the upper face ofsaid disc members along concentric annular paths, said cam means havingcam portions located along said paths at angularly spaced of 36* ormultiples thereof, whereby after one complete turn of said disc memberall the weights of the entire weights decade have been raised.
 4. Adevice as claimed in claim 1, wherein said guiding means comprise twocrosspieces arranged at right angLes to each other in a substantiallyhorizontal plane above said disc members, said crosspieces each havingpairs of through bores for receiving respective pairs of said pins, eachpair of said pins engaging one of said weights at diametrically oppositepoints, the pairs of pins relative to adjacent weights being disposedalternatively in the one and the other of said crosspieces.
 5. A deviceas claimed in claim 1, wherein at least one of said disc members has anexternal cam comprising two cam portions arranged opposite to each otheralong annular concentric pathes of slightly different radii and eachextending for a half of its circumference, with each of said camportions being associated one pin comprising an upper and a lower shank,the shanks of one of said pins being coaxial to each other and theshanks of the other of said pins being off-centered, whereby the saidupper shank engages the corresponding one of said annular weights andthe said lower shank engages the corresponding one of said two camportions.
 6. A device as claimed in claim 5, further comprising a springinterposed between said upper and said lower shank.